The use of collimator angle optimization and jaw tracking for VMAT‐based single‐isocenter multiple‐target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system

Abstract

Island blocking occurs in single-isocenter multiple-target (SIMT) stereotactic radiotherapy (SRS) whenever targets share multi-leaf collimator (MLC) leaf pairs. This study investigated the effect on plan quality and delivery, of reducing island blocking through collimator angle optimization (CAO). In addition, the effect of jaw tracking in this context was also investigated. Methods: For CAO, an algorithm was created that selects the collimator angle resulting in the lowest level of island blocking, for each beam in any given plan.Then, four volume-modulated arc therapy (VMAT) SIMT SRS plans each were generated for 10 retrospective patients: two CAO plans, with and without jaw tracking, and two plans with manually selected collimator angles, with and without jaw tracking. Plans were then assessed and compared using typical quality assurance procedures.Results: There were no substantial differences between plans with and without CAO. Jaw tracking produced statistically significant reduction in low-dose level parameters; healthy brain V10% and mean dose were reduced by 9.66% and 15.58%, respectively. However, quantitative values (108 cc for V10% and 0.35 Gy for mean dose) were relatively small in relation to clinical relevance.Though there were no statistically significant changes in plan deliverability, there was a notable trend of plans with jaw tracking having lower gamma analysis pass rates. Conclusion:These findings suggest that CAO has limited benefit in VMAT SIMT SRS of 2-6 targets when using a low-dose penalty to the healthy brain during plan optimization in Eclipse. As clinical benefits of jaw tracking were found to be minimal and plan deliverability was potentially reduced, a cautious approach would be to exclude jaw tracking in SIMT SRS plans. How to cite this article: Pudsey LMM, Cutajar D, Wallace A, et al. The use of collimator angle optimization and jaw tracking for VMAT-based single-isocenter multiple-target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system.

Fast stereotactic radiosurgery planning using patient-specific beam angle optimization and automation

“…These were chosen by the planner using visual assessment of the target locations in the beams-eye-view, resulting in a closer approximation to the optimal solution than using a fixed angle approach. Similar results were reported in a study by Pudsey et al [28] which compared optimized to manually selected collimator angles for VMAT-based single-isocenter multiple-target SRS with a retrospective cohort of 10 patients. They found no significant differences between plans with or without collimator optimization.…”

“…Past studies have shown various ways to solve the island-blocking problem and compared to a number of different planning methods [7] , [8] , [22] , [28] . This study shows how beam angle optimization can be clinically implemented using a treatment planning system API to increase efficiency while maintaining plan quality.…”

Radiosurgery for Five to Fifteen Brain Metastases: A Single Centre Experience and a Review of the Literature

“…A series of SI-VMAT plans for more than five brain metastases generated with 5mm MLCs reported comparatively poor GIs of 5.0 -5.6 ( 51 ). According to Ohira et al, optimization of the collimator angle ( 52 ) can achieve better sparing of healthy brain, although additional jaw tracking did not yield a benefit ( 53 ). The better GIs achieved with the DCA than with VMAT stem from its development as an extension of radiosurgery with conical collimators, but come at the cost of conformity in the case of non-spherical targets ( 54 ).…”

Optimization of collimator angle combined island blocking with parked gap achieves superior normal tissue sparing in SBRT planning of multiple liver lesions

“…However, most of the previous studies 6 , 7 , 8 , 9 , 10 , 11 , 16 , 17 regarding collimator angle optimization only considered the IB problem and neglected the PG problem. Therefore, in this study, we developed a new collimator angle optimization algorithm that combined the IB and PG areas to fully represent the unnecessary open space area of MLC.…”